This invention relates to packaging structure, and more particularly to packaging structure for foods affording refrigerated storage and subsequent heating to prepare the food for serving.
In the preparation of refrigerated packaged food for serving in a heated state, it has been a practice to place the packaged food in a microwave oven to heat the same. Heating may be either for the purpose of thawing and cooking frozen food or for thawing and heating cooked foods. In either event, considerable water vapor pressure is generated, and since packages are usually well sealed while stored, precautions must be taken to ensure against sudden explosion of the package resulting possibly in damage to the oven or even injury to the user. One useful structure for packaging foods of the aforementioned type comprises a tray including bottom an side walls, and a transparent film of plastic material stretched over and sealed to the side wall. Venting such packages has, in the past, involved provision of means for venting in response to water vapor pressure build-up. Such means could, of course, in themselves vent with a suddeness resulting in food leakage. An example of a pressure responsive vent is found in U.S. Pat. No. 4,013,798 believed material to the examination of this application. The patent discloses a food tray 10, a cover 31 sealed thereover, and a vent notch 32 in the tray in the region of the cover seal. Presence of notch 32 weakens the seal so that it will rupture upon build-up of water vapor pressure.
U.S. Pat. No. 3,353,968 also is believed material to the examination of this application in its teaching of a food package 54 provided with conductive strips 62 for concentrating microwave energy in the packaged food.
It is an objective of the present invention to provide improved automatic venting means for a sealed food package adapted to undergo heating by microwave energy.
It is a further objective of the invention to provide improved venting means for a sealed food package operable automatically upon subjection of the package and its contents to heating by microwave energy.
It is a still further objective of the invention to provide improved venting means for a sealable food package adapted to undergo heating by microwave energy, which venting means is provided automatically upon heating and independently of pressure build-up.